Internal combustion two-stroke power unit

ABSTRACT

An internal combustion, two-stroke power unit having a cylinder element mounted for reciprocation in a base and a piston element mounted for reciprocation in the cylinder element, said elements reciprocating relative to each other in opposite directions, interconnecting means between the two elements to cause them to reciprocate in phase with each other, power take-off means connected to one of these elements, and an arrangement for automatically throttling the unit when it is operating under partial- and no-load conditions.

United States Patent [191 Fandrich 45] May 8, 1973 [54] INTERNAL COMBUSTION TWO- STROKE POWER UNIT [75] Inventor: Helmut E. Fandrich, Vancouver,

British Columbia, Canada [73] Assignee: Dueck Building Supplies Ltd.,

British Columbia, Canada 221 Filed: Feb. 18, 1971 21; App1.No.:116,339

[52] U.S. CL... ...l23/50 B, 123/46 R, 123/71 R [51] Int. Cl ..F02b 59/00 [58] Field of Search ..123/50 R, 50 A, 50 B, 123/46 SC, 46 B, 46 A, 46 R, 197 C, 71 R,

[56] References Cited UNITED STATES PATENTS 928,405 Simmon 123/50 R 968,166 8/1910 Knight "123/50 R 1,278,571 9/1918 Bell r r "123/50 R 1,781,704 11/1930 Reynolds.. ..,..l23/5() R 3,192,972 7/1965 Tenney ..l43/68 Primlzry Examiner-Wendell E. Burns Attorney-Fetherstonhaugh & Co.

[57] ABSTRACT An internal combustion, two-stroke power unit having a cylinder element mounted for reciprocation in a base and a piston element mounted for reciprocation in the cylinder element, said elements reciprocating relative to each other in opposite directions, intercon necting means between the two elements to cause them to reciprocate in phase with each other, power take-off means connected to one of these elements, and an arrangement for automatically throttling the unit when it is operating under partialand no-load conditions.

36 Claims, 10 Drawing Figures PATENTEU MY 81975 SHEET 1 OF 4 INVENTQR HELMUT E. FANDRICH ATTORNEYS PATENTED 81975 3.731.662

SHEET 2 BF 4 INVENTOR HELMUT E. FANDRICH AT TORNEIS PATENTEUHAY 8% 3.731562 'SHEET u {1F 4 INVENTOR HELMUT E, FANDRICH ATTORNEY INTERNAL COMBUSTION TWO-STROKE POWER UNIT BACKGROUND OF THE INVENTION This invention relates to internal combustion, twostroke power units which may be used for many different purposes.

There are many two-stroke power units or engines in the prior art. The use of the prior engines is to a degree 0 SUMMARY OF THE INVENTION One form of power unit according to the present invention includes a cylinder element mounted for reciprocation in a base, and a piston element mounted for reciprocation in the cylinder element. These elements are adapted to reciprocate relative to each other in opposite directions. The unit also includes interconnecting means between the piston element and the cylinder element to balance the mass of the piston element with the mass of the cylinder element during relative reciprocation of said elements to reduce vibration. Power takeoff means is connected to one of these elements and is operable on relative reciprocation thereof. Said interconnecting means is such that the mass of the piston element and whatever is connected to move therewith can be substantially balanced with the mass of the cylinder element and whatever moves therewith so that, although this is an internal combustion engine, there is little vibration and no back thrust within the unit itself.

An alternative form of the invention includes a port arrangement that automatically functions to throttle the unit when it is operating without under partial or no load. This unit includes a cylinder mounted for reciprocation in a base and having a power chamber at one end and a precompression chamber at the opposite end, and a piston is mounted in this cylinder for reciprocation therein. The cylinder and piston move away from each other during a power stroke when a fuel charge is fired in the power chamber. At this time, a fuel mixture in the precompression chamber is compressed by the piston, and some of the fuel mixture is moved under pressure into a transfer port or passage. As the piston progresses, it opens an exhaust port and at the same time or just after this, it opens the transfer port or passage to allow the fuel charge therein to flow into the power chamber. Suitable means is provided for moving the piston back through a compression stroke. For example, the piston can compress a spring in the precompression chamber end of the cylinder which after the power stroke, returns thepiston through the compression stroke. If the unit is under load, the operation continues as just described. However, if the unit is not under full load or any load, the piston on the power stroke can travel in the precompression chamber far enough to close off the transfer port and to partly or completely open an auxiliary port in the chamber wall to relieve the pressure of the fuel charge therein. As a result of this, fuel entering the transfer passage is not compressed as much as when the unit is under full load so that the power chamber actually receives a smaller fuel charge. Thus, the power unit is effectively throttled down at this time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic longitudinal section through one form of power unit in accordance with this invention, showing the piston at the beginning of a power stroke,

FIG. 2 is a fragmentary view similar to FIG. 1 showing the piston at the end of the power stroke when the unit is under load,

FIG. 3 is a view similar to FIG. 2' showing the piston at the end of the power stroke when the unit is under no load,

FIG. 4 is a reduced side elevation partly in section, of the unit of FIG. 1,

FIG. 5 is a diagrammatic longitudinal sectional view through an alternative form of power unit,

FIG. 6 is a fragmentary view similar to FIG. 5 showing a power unit which is a variation of the alternative of FIG. 5,

FIG. 7 is a diagrammatic longitudinal section through another alternative form of power unit,

FIG. 8 is a fragmentary view of yet another alternative which is a slight variation of that of FIG. 7,

FIG. 9 is a fragmentary diagrammatic longitudinal section through a power unit similar to that of FIG. I, but including a different latching arrangement, and showing the various elements when the piston is at the end of a power stroke, and

FIG. 10 is an enlarged isometric view of the latching arrangement of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 to 4 of the drawings, 10 is an internal combustion two-stroke power unit in accordance with the present invention and including a base 12 having a relatively large end 14 with an outer cylinder 16 connected thereto and projecting outwardly therefrom. This 'outer cylinder has an outer head or end 17. An elongated inner cylinder 20 is mounted on base 12 for reciprocation relative thereto, said inner cylinder having a head 21 at one end within the outer cylinder and forming a power chamber 23 within cylinder 20. A precompression chamber 26 is formed in cylinder 20 at the opposite end thereof, said end being closed by an end wall 27. In this example, cylinder 20 is formed with an enlargement 29 substantially midway between the ends thereof which slidably bears against the inner surface of outer cylinder 16 of base 12. This enlargement 29 separates the interior of cylinder 20 from the interior of end 14 of the base, and it is preferable to provide sealing means in the outer surface of the enlargement, such as a sealing ring 32. In the preferred form of this embodiment, inner cylinder 20 is smaller incross section than outer cylinder 16, and the former has cooling fins 34 on its outer surface which slide along the inner surface of the outer cylinder. If fins 34 are omitted, the inner cylinder slidably fits in the outer cylinder, and enlargement 29'is not required. Additional cooling fins 35 can be on head 21 and project outwardly therefrom, and these fins are adapted to fit into slots 36 within outer cylinder head 17.

A piston 40 is mounted in cylinder for reciprocation therein, and includes a head 41 with a skirt 42 projecting away therefrom. This skirt preferably has a port 43 therein near head 41. A piston rod 44 is connected to piston 40 and extends longitudinally through precompression chamber 26 and slidably through end wall 27 and end 14 of base 12. Sealing rings 45 and 46 are provided around the piston rod at wall 27 and end 14, respectively. The outer end of piston rod 44 forms power take-off means 48. Spring or other means urges piston 40 towards head 21 of inner cylinder 20, and in this example, inner and outer springs 50 and 51 are provided for this purpose, said springs surrounding piston rod 44 within chamber 26 and extending between piston head 41 and the chamber end wall 27.

When a fuel charge is fired in power chamber 23, cylinder 20 and piston 40 move away from each other, and compress springs 50 and 51. It is desirable to cause the cylinder and piston to move in phase with each other, and this is accomplished in this embodiment by means of a segment gear 55 mounted on a shaft 56 which extends laterally from the gear and is carried by end 14 of base 12. Piston rod 44 is formed with a rack section 58 which meshes with teeth 59 of gear 55, while additional teeth 60 of this gear on the opposite side of shaft 56 from teeth 59 mesh with the teeth ofa rack 62 which is connected to enlargement 29 of cylinder 20 at 63. In the preferred form of this embodiment, the teeth 59 of gear 55 are positioned farther away from shaft 56 than the teeth 60 of said gear.

Segment gear 55 and racks 58 and 62 meshing therewith are intended to balance the mass of piston 40 and the parts that move therewith with the mass of cylinder 20 and the parts that move with it. As the mass of cylinder 20 and its associated parts is considerably greater than that of piston 40 with the parts that move with it, it is necessary to utilize leverage to offset this in order to get the proper balancing effect. The ratio of the distance between the center of shaft 56 and teeth 59, and the center of said shaft and teeth 60 is adjusted to offset these different masses. In other words, gear 55 acts as a lever, the fulcrum of which is so located that the turning moment of the two masses about said fulcrum is equal.

Fuel for operating this engine is supplied in any desired manner. In this example, a suitable carburetor 65 is mounted on base 12 and positioned to direct an air-fuel mixture through port 66 into end 14 of base 12. An intake port 69 is provided in the wall of cylinder 12 where it is uncovered by piston 40 when the latter nears the end ofits compression stroke. A transfer passage or port 71 is formed in enlargement 29 on the opposite side of the cylinder from intake port 69. This passage or port is relatively long and is positioned so that the end 72 thereof opens into power cylinder 23 as piston 40 nears the end of its power stroke. Opposite transfer passage end 72 is an exhaust port 74 formed in cylinder 20 at a position where this port is uncovered at the same time as or just before transfer passage end 72 is brought into communication with the power chamber.

The fuel charges are fired in chamber 23 when piston 40 is near the end of its compression stroke in any desired manner, such as by compression, or by means ofa spark plug 78 shown in broken lines in FIG. I. This spark plug would be fitted into cylinder head 21, and

would project through an opening in the outer cylinder head 17.

In FIG. 1, piston 40 is ready for its power stroke. The compressed fuel in chamber 23 is fired, and piston head 41 and cylinder head 21 move away from each other under the force of the expanding gases, segment gear 55 keeping these elements in phase, and balancing the mass of one with the mass of the other. As the piston nears the end of its power stroke, it uncovers exhaust port 74 to allow the combustion gases to flow therethrough. The end 72 of transfer passage 71 is also uncovered, and the fuel charge under pressure trapped in this passage flows into power chamber 23 and helps to expel the exhaust gases. When piston skirt 42 first closes off the transfer passage during the power stroke, precompression chamber 26 remains in communication with the transfer passage through skirt port 43 until the piston reaches the end of its full-power stroke. When piston 40 reaches the position shown in FIGv 2, it is substantially at the end of its power stroke when the unit is under full load. During the power stroke, fuel is compressed in chamber 26 after piston skirt 42 closes intake port 69. At the same time, springs 50 and 51 are compressed within chamber 26. At the end of the power stroke, springs 50 and 51 reassert themselves to move piston 40 through its compression stroke. During this stroke, the transfer passage 71 is in communication with the precompression chamber first through skirt port 43 and then when the outer end of skirt 42 clears said passage so that the latter fills with fuel under pressure at this time. As soon as the piston closes off the transfer passage and the exhaust port, the fuel in chamber 23 is compressed for firing for the next power stroke.

The power unit or engine described so far can be controlled in the usual manner by means of a throttle valve controlling the fiow of fuel from carburetor 65. However, it is preferred to eliminate this necessity. In this case, an auxiliary port 81 is provided in cylinder 20 near transfer passage 71 but on the precompression chamber side thereof. FIG. 2 shows the piston at the end of its power stroke when the power unit is under full load. However, if there is only a partial load or no load, the piston will travel further into precompression chamber 26 before reaching the end of its power stroke. When this happens, port 43 in skirt 42 partly or substantially completely registers with auxiliary port 81 so that the interior of the precompression chamber is brought into communication with the interior of base end 14. This drops the pressure of the fuel mixture in the precompression chamber. As a result of this, the pressure of the fuel mixture entering transfer passage 71 when the latter is in communication with the precompression chamber is lower than it otherwise would be so that the mixture directed into power chamber 23 is under lower pressure. The pressure drop in chamber 26 depends upon the amount of overlap of ports 43 and 81 so that the power unit is effectively throttled as the load approaches the vanishing point.

Another effect from this port arrangement is that when port 43 registers with port 81, the compressed fuel mixture which flows into the base causes some of the mixture to flow back into the carburetor. This tends to enrich the mixture, and this is desirable under noload or part-load conditions.

Power unit can be used for any desired purpose. In this example, a saw blade 85 is connected to power take-off means 48 at the outer end of piston rod 44. The teeth of this blade can be such as to cut during the power stroke of piston 40 or during the compression stroke thereof under the action of springs 50 and 5 1. As an alternative, the saw blade can be connected to cylinder so as to be reciprocated thereby. As another alternative, shaft 56 might constitute the power take-off means, in which case, whatever is to be driven by the power unit would be suitably connected to this shaft. This shaft can operate a one-way clutch to provide a rotary motion instead of a reciprocatory motion for whatever is to be driven by the power unit.

As stated above, cylinder 20 reciprocates relative to and in opposition to piston 40. When cylinder 20 is mounted in an outer cylinder 16, as shown, it acts as a pump during reciprocation within the outer cylinder so that air flows over the outer surface of the inner cylinder for cooling purposes.

Power unit 10 can be stopped or started in any desired manner. It is preferable to stop the movement of piston 40' when it is near the end of its power stroke and to lock the piston in this position. When this is done, when the piston is again released, springs 50 and 51 will urge the piston along its compression stroke, and there is preferably sufficient energy stored in the springs to cause the piston to reciprocate several times so that the power unit or engine will start.

FIG. 4 illustrates one way of doing this. In this example, a shaft 87 projects outwardly from the side of base end 14. This shaft has a gear 88 on its inner end meshing with teeth 89 formed on rack section 58 of piston rod 44, see FIG. 1. An arm 92 is fixedly secured to the outer end of shaft 87 and hangs downwardly therefrom. A grip or handle 94 is secure to base 12, and a control level 95 is pivotally mounted at 96 on said base near grip 94. Lever 95 is formed with a projection 98 which extends from pivot 96 beneath the lower end of arm 92 and is urged against the latter by a spring 99. Projection 98 is formed with ratchet teeth 101 along its upper surface which are engageable by the lower end of arm 92. These teeth are inclined so that when engaged by arm 92 they permit said arm to swing in the direction of arrow 102, but prevent the arm from swinging in the opposite direction.

When arm 92 is in the position shown in FIG. 4 and gripped by the teeth 101 of lever projection 98, piston 40 is retained at the end of its power stroke. When it is desired to start and use power unit 10, the operator grips handle 94 and squeezes control lever 95 which disengages teeth 101 from arm 92, leaving the latter free. At this time, springs 50 and 51 exert themselves, and the power unit is started. When it is desired to stop the unit, control lever 95 is released, and teeth 101 will grip arm 92 when the piston reaches the end of its power stroke.

FIG. 5 illustrates an alternative power unit 110 which is similar to unit 10, but has a piston and cylinder arrangement in place of compression springs 50 and 51.

Power unit 110 includes a base 112 with aligned cylinders 114 and 115 slidably mounted therein. Suitable means is provided for connecting these cylinders together so that they will move as a unit. The cylinders may be rigidly interconnected, or they may be connected by means of a compression spring 118 surrounding a housing 119 within and fixedly secured to base 112 in any convenient manner. Pistons 121 and 122 are mounted for reciprocation in cylinders 114 and between opposed heads 124 and 125 thereof. Suitable means is provided for connecting pistons 121 and 122 so that they will move together, such as by means of a piston rod 127 which slidably extends through end walls 128 and 129 of housing 119. Piston 121 has a head 129 and a skirt 130, while piston 122 has a head 132 and a skirt 133. Piston 121 reciprocates between cylinder head 124 and a wall formed by a sleeve 135 connected at one end 136 to cylinder 114 and an opposite free end 137. Ports 138 are formed in end 137 and are normally covered by flap valves 140. These valves open away from sleeve 135 into a precompression chamber 143 positioned between said sleeve or wall and head 129 of the piston. Skirt 130 of the piston moves back and forth in an annular space 145 located between sleeve 135 and the adjacent portion of cylinder 114.

Similarly, piston 115 reciprocates between cylinder head 125 and a wall formed by a sleeve 148 having an end 149 with ports 150 therein controlled by flap valves 152, said valves opening into precompression chamber between piston head 132 and wall or sleeve 148. Skirt 122 of piston 115 moves in an annular space 157 between sleeve 148 and the adjacent surface of cylinder 115. Power chambers 158 and 159 are formed within cylinders 114 and 115 between heads 124 and 125 thereof and the pistons operating in these cylinders. Fuel charges are fired in the power chambers in any convenient manner, such as by means of spark plugs 161 and 162 located in heads 124 and 125.

When a charge is fired in power chamber 158, piston 121 and cylinder 114 move away from each other, said piston moving on a power stroke. This moves piston 122 and cylinder 115 towards each other, the latter piston being moved on a compression stroke. When a charge is fired in power chamber 159, the opposite action takes place.

Suitable means is provided for balancing the mass of the two pistons and the parts moving therewith and the mass of cylinders 114 and 115 and the parts moving therewith. In this example, piston rod 127 is formed with a rack section 165 which meshes with teeth 166 of a segment gear 167 fixedly mounted on a shaft 168 which is carried by base 112. The teeth 166 are on a long section of gear 167, and teeth 170 are formed on a short section of said gear on the opposite side of shaft 168 from teeth 166. Teeth 171 mesh with rack teeth 170 which are connected to cylinders 114 and 115 in any convenient manner. In this example, the rack of teeth 171 is connected to spring 118 substantially midway betwcen the end thereof. Segment gear 167 acts as a lever, the fulcrum of which is such that the turning moment of the mass of the pistons and of the mass of the cylinders about said fulcrum is even.

Cylinder 114 has an exhaust port 175 therein which is uncovered by piston 121 when the latter is near the end of its power stroke. An elongated transfer port or passage 177 is provided in the cylinder opposite te exhaust port, and said passage or transfer port has an end 178 which is uncovered by the piston skirt when the piston is near the end of its power stroke. Similarly,

cylinder 1 is provided with an exhaust port 181 and a transfer port or passage 182 having an end 183 which is uncovered when piston 122 nears the end of its power stroke.

Fuel is directed into precompression chambers 143 and 155 in any convenient manner. In this example, a suitable carburetor 186 is mounted on base 112 and is adapted to direct air-fuel mixtures through a passage 187 into housing 119 which forms a plenum chamber 188. Ports 190 and 191 in end walls 128 and 129 of housing 119 are controlled by flap valves 193 and 194 which open away from plenum chamber 188.

In FIG. 5, piston 121 is at the end of its compression stroke, while piston 122 is at the end of its power stroke. When the change in power chamber 158 is fired, piston 121 moves through its power stroke, moving piston 122 through its compression stroke. This movement of piston 122 draws fuel through ports 191 and 150 into precompression chamber 155. At the same time, fuel in precompression chamber 143 and transfer port or passage 177 is compressed. When piston 121 clears exhaust port 175 the exhaust gases flow out of the latter, and when said piston clears end 178 of the transfer port or passage, the compressed fuel flows into chamber 158. This same action takes place when the charge in power chamber 159 is fired to move piston 122 through its power stroke and piston 121 through its compression stroke. Fuel is drawn into precompression chamber 143 through ports 190 and 138 at this time.

Suitable power take-off means is provided for power unit 110. In this example, shaft 168 acts as a power shaft. It is oscillated around its longitudinal'axis. If desired, a one-way ratchet 196 may be rotated by this shaft in order to provide rotational movement in the same direction for any suitable purpose.

FIG. 6 illustrates another alternative power unit 210 which is similar to and operates somewhat in the same manner as unit 110, the main difference being in the I power take-off means.

In unit 210 there is a base 212 upon which opposed cylinders 214 and 215 reciprocate, said cylinders being connected for movement together by a housing 216. Pistons 218 and 219 reciprocate in cylinders 214 and 215, and are interconnected by a piston rod 222. A segment gear 225 on a shaft 226 carried by base 212 has teeth 228 meshing with the teeth of a rack section 229 in piston rod 222, and teeth 232 meshing with the teeth of a rack section 233 connected to housing 216.

Fuel is directed into housing 216 in any convenient manner, and said housing is connected by intake ports 236 and 237 to the interiors of cylinders 214 and 215. Said cylinders 214 and 215 have exhaust ports 239 and 240, and transfer ports or passages 242 and 243, respectively. The fuel is fired in cylinders 214 and 215 in any suitable manner, such as by means of spark plugs 245 and 246.

Unit 210 operates in the same manner as unit 110. However, the power take-off of unit 210 consists of a piston 248 mounted for reciprocation in a cylinder 249 connected to and opening into base 212, said cylinder extending substantially at right angles to piston rod 222. A piston rod 250 is connected to pistons 248 and slidably extends through the outer end of cylinder 249, said piston rod 250 providing power take-off means for the unit. In this example, a saw blade 252 is connected to for reciprocation by piston rod 250.

Piston 248 is reciprocated in its cylinder by a connecting rod 256 which is connected at one end to said piston by a pin 257, and at its opposite end to rack section 229 of piston rod 222 by another pin 258. The length of connecting rod 256 is such that as piston rod 222 reciprocates, piston 248 is reciprocated in its cylinder.

If desired, piston 248 may be used to direct fuel into base 212. For this purpose, cylinder- 249 is provided with an intake port 262 near the inner end thereof, said port being connected to a suitable carburetor, not shown. When piston 248 is at the inner end of its stroke, it closes port 262, but when said piston is at the outer end of its stroke, the port is uncovered to permit fuel to flow into base 212, said fuel being compressed slightly by the piston as it moves inwardly in its cylinder. Base 212 is in communication with the interior of housing 216 through ports 264.

FIG. 7 illustrates another alternative form of power unit 310. This unit is similar to units and 210 in that it has aligned and interconnected cylinders mounted for reciprocation on a base 322, and interconnected pistons reciprocally mounted in said cylinders, but for the sake of convenience, the piston and most of the cylinder at the right end of the unit have been omitted from the drawing, since these are only duplicates of those at the left end.

A cylinder 314 has a piston 317 reciprocally mounted therein, said cylinder being connected with a cylinder at the opposite end of the unit by a sleeve 319. A portion of the opposite cylinder is shown at 321. Piston 317 is connected to the piston at the opposite end of the unit by a connecting rod 323 which has a relatively long enlarged section 327 centrally thereof with a slot 328 therein. Cylinder 314 is provided with an intake port, exhaust port, and transfer passage or port similar to those described above. The main difference between power unit 310 and the others is in the means for balancing the masses of the pistons and associated parts with the masses of the cylinders and their associated parts, as well as the power take-off means.

In this example, a crank or lever arm 332 is fixedly mounted on a drive shaft 333 carried by base 322. This arm has a long section 335 extending from shaft 333 into slot 328 of connecting rod section 327, and the outerend of this section 335 is connected by a pin 336 to a connecting link 337, the opposite end of which is connected by a pin 338 to rod section 327. Arm 332 also has a short section 340 extending from shaft 333 on the opposite side thereof from long section 335, the outer end of said short section being connected to sleeve 319 of the cylinders in any desired manner. In this example, a compression spring 342 extends between lever section 340 and a bracket 343 secured to and extending outwardly from sleeve 319. One end of spring 342 is connected to the short section of arm 332 at 344. Crank or lever arm 332 and the short and long sections thereof and link 337 form linkage between the two pistons and the two cylinders.

Similarly, a crank or lever arm 346 is fixedly mounted on a shaft 347 carried by base 322, said arm having a long section 348 connected by a link 349 to connecting rod section 327, and a short section 352 connected to cylinder 319 through a compression spring 353 extending between said section 352 and a bracket 354 projecting from said cylinder. One end of spring 353 is connected to 355 to the short section of arm 346. Crank or lever arm 346 is effectively connected to cylinder 314 through cylinder 321, and sleeve 319.

Power can be taken off either or both of the shafts 333 and 347. If rotational action is required, one-way ratchets 357 and 358 are mounted on shafts 333 and 347, said ratchets acting opposite to each other.

Fuel is supplied to the cylinders of unit 310 in any convenient manner. In this example, a suitable carburetor 360 is mounted on a base 322 and communicates with a port 361 in said base. A throttle plate 362 is connected to cylinder 314 to reciprocate therewith along the surface 'of base 322 at port 261. This plate has ports 365 and 366 therein on opposite sides of a wall 367 which extends to sleeve 319 and part of cylinder 314 to divide interior of base 322 into base chambers 369 and 370.

When piston 317 is at the end of its power stroke, plate port 365 is in registry with base port 361 to permit fuel to flow into chamber 369, said fuel flowing through an intake port 373 into the precompression chamber 374 of cylinder 314. When the opposite piston is at the end of its power stroke, plate port 366 is in registry with base port 361 so that fuel can flow into chamber 370 and from there into the precompression chamber of the opposite cylinder.

FIG. 8 illustrates part of an alternative power unit 310a which is practically the same as unit 310. In 310a, springs 342 and 353 have been omitted, and crank or lever arm 332 is connected to bracket 343 of sleeve 324 by a link 384 which is connected to the short end of arm 332 by pin 385 and to said bracket 343 by another pin 386. Similarly, crank or lever arm 346 is connected to bracket 354 of cylinder 321 by a link 389. One end of this link is connected to the short end of arm 346 by a pin 390, and the opposite end of said link is connected by another pin 392 to bracket 354.

Power unit 310a operates in the same manner as unit 310, excepting that the crank or lever arms 332 and 346 are more or less rigidly connected to the cylinders through links 384 and 389, instead of being resiliently connected thereto by springs 342 and 353 of unit 310.

FIGS. 9 and 10 illustrate a latching arrangement 400 which is an alternative to the latching arrangement illustrated in FIG. 4 for the embodiment of the invention of FIG. 1. Arrangement 400 is shown and described relative to FIG. 1, but it is to be understood that it could be used in any of the other embodiments.

The power unit 1011 of FIG. 9 is substantially the same as unit 10, excepting that the segment gear 55a for causing the cylinder and piston of the unit to move in phase with each other is located above piston rod 44. Gear 55a meshes with teeth 58a in the piston rod and with teeth 402 formed in an extension 403 of cylinder 20.

Latch arrangement 400 includes a latch arm 406 Connected at one end to the end of cylinder by a pin 407, and having ratchet teeth 408 on its opposite end. A slide 412 is mounted on arm 406 and is connected by pins 413 to an extension 414 ofa lever 415. Extension 414 is swingably connected to this lever by pins 417.

Lever 415 is swingably mounted on pivot pins 419 carried by a bracket 420 mounted on base 12 beneath piston rod 44. The pins 413 of slide 412 extend through vertical slots 422 in extension 414. A spring 424 is connected to the upper end of extension 414 at one end and at its opposite end to the end 14 of the base, see FIG. 9.

The teeth 408 of the latch arm are adapted to engage corresponding ratchet teeth 426 in piston rod 44. Ratchet teeth 408 and 426 are such that when they are in engagement they will stop piston rod 44 from moving inwardly with respect to the power unit so that this prevents cylinder 20 and piston from moving towards each other. The location of teeth 426 on the piston rod is such that they are engaged by latch teeth 408 when the piston is at the end of a power stroke or, in other words, when the ends of the piston and cylinder are at the extremities of their movement away from each other.

A spring 430 connected to slide 412 at 431 curves under and upwardly relative to the slide, and has an end normally in notch 432 in arm 406 near teeth 408. This spring fastens the slide to the latch arm so that the motion of the arm can extend spring 424 and rotate lever 415 to force the latch arm upwardly against rod 44. When this is done,'the piston rod can move outwardly because of the set of the rachet teeth, but inward movement thereof is prevented when teeth 408 engage rod teeth 426.

In another arrangement the bracket 420 is mounted on an extension to cylinder 20, and the end 431 of spring 430 is mounted on frame 12 instead of on slider 412 and notch 432 is in slider 412 instead of in arm 406.

Suitable means is provided for selectively withdrawing the end of spring 430 from notch 432. In this example, a cable 435 is connected to the spring adjacent the free end thereof and extends downwardly through a hole 436 in base 12 into grip 94. The opposite end of this cable is connected to a trigger 438 which is swingably connected to the base by a pin 439, said trigger extending downwardly through a slot 440 formed in the grip and out of the latter. Although not absolutely necessary, a spring 442 may be provided for normally maintaining the trigger in an upper or advanced position.

In order to start the motor unit, it is only necessary to pull trigger 438, and this draws the free end of spring 430 out of notch 432. Once the spring is free of the notch, spring 424 becomes operative and pulls extension 414 clockwise through an are about pin 417, pulls lever 415 clockwise through an are about pin 419 and pulls slide 412 along latch arm 406. When pin 413 reaches the end of slot 422, the clockwise movement of lever 415 urges the latch arm 406 down away from piston rod 44 and separates teeth 408 from teeth 426. The compressed springs 50 and 51 reexert themselves, moving the piston and cylinder through a compression stroke. As long as the trigger is held down, the lever 415 will be held at a clockwise angle from the vertical by the force of spring 424 so that the power unit will continue to operate. But once trigger 438 is released, spring 430 enters slot 432 when piston 44 and cylinder 20 are near the end of a compression stroke. When the spring is in the slot and while the piston and cylinder Ill move apart on the power stroke, the latch arm 406 and slide 412 move to the left. The leftward motion of the slide extends spring 424 and rotates extension 414 and lever 415 counterclockwise toward a vertical position. The counterclockwise rotation of lever 415 rotates the latch arm 406 counterclockwise about pin 407 and brings latch teeth 408 in contact with rod teeth 426. While latch arm 406 moves left and piston rod 44 moves right, latch teeth 408 will ride over rod teeth 426. The pivotal connection of extension 414 to lever 415 permits the latch arm and slide 412 thereon to move downwardly against the tension of spring 424 when teeth 426 ride over latch teeth 408. When the piston reaches the end of its power stroke, teeth 408 and 426 are in engagement, and this prevents the piston from returning so that the springs 50 and 51 are held under compression and spring 424 is held under tension. At this time, the power unit a in inoperative.

I claim:

1. In an internal combustion, two-stroke power unit, a base, a cylinder element mounted for reciprocation in the base, a piston element mounted for reciprocation in the cylinder element, said piston and cylinder elements being moved away from each other on a power stroke when a fuel charge is fired in the cylinder element resilient means between the piston and cylinder elements and positioned to be compressed during said power stroke, said resilient means after the power stroke moving said elements towards each other through a compression stroke, interconnecting means between the cylinder element and the piston element to cause said elements to work in phase with each other, and power take-off means connected to one of said elements operable on relative reciprocation of the piston and cylinder elements, said interconnecting means comprising a rack connected to the piston element and a segment gear eccentrically mounted on a shaft carried by the base, said segment gear having first teeth meshing with said rack and second teeth closer to said shaft than the first teeth and meshing with a rack connected to the cylinder element.

2. In an internal combustion two-stroke power unit, a base, a cylinder element mounted for reciprocation in the base, a piston element mounted for reciprocation in the cylinder element, said piston and cylinder elements being moved away from each other on a power stroke when a fuel charge is fired in the cylinder element, resilient means between the piston and cylinder elements and positioned to be compressed during said power stroke, said resilient means, after the power stroke, moving said elements towards each other through a compression stroke, oscillatory interconnecting means between the cylinder element and the piston element to cause said elements to move in phase with each other while permitting variations in the lengths of said power stroke and said compression stroke; and power take-off means connected to one of said elements operable on relative reciprocation of the piston and cylinder elements, said cylinder element being slidably mounted in an outer cylinder forming part of the base, a piston element mounted for reciprocation in the cylinder element, said piston and cylinder elements being moved away from each other on a power stroke when a fuel charge is fired in the cylinder element resilient means between the piston and cylinder elements and positioned to be compressed during said power stroke, said resilient means after the power stroke moving said elements towards each other through a compression stroke, oscillatory interconnecting means between the cylinder element and the piston element to cause said elements to move inphase with each other while permitting variations in the lengths of said power stroke and said compression stroke, and power take-off means connected to one of said elements operable on relative reciprocation of the piston and cylinder elements, said cylinder element having a head at one end and a precompression chamber at the opposite end thereof and including an intake port in the cylinder element to direct a combustible fuel into said precompression chamber when said piston element is near said head, a transfer passage for directing said fuel under pressure from the precompression chamber into the cylinder element between said head and the piston element during said power stroke, and an exhaust port in the cylinder element positioned to exhaust gas from said cylinder element when the piston element nears the end of the power stroke.

4. A power unit as claimed in claim 3 in which said piston element has a skirt opening towards said precompression chamber, said skirt having a port therein positioned to keep the transfer passage in communication with the precompression chamber during at least part of the power stroke.

5. A power unit as claimed in claim 4 in which said skirt port is positioned substantially to register with an auxiliary port in the precompression chamber as the piston element moves about as far as possible on the power stroke to relieve the pressure in the precompression chamber.

6. In an internal combustion, two-stroke power unit, a base, an elongated cylinder mounted for reciprocation in the base, a piston mounted for reciprocation in the cylinder and dividing said cylinder into a power chamber and a precompression chamber, a piston rod connected to the piston and extending through and out from the precompression chamber, said piston and cylinder being moved away from each other on a power stroke when a fuel charge is fired in the power chamber, oscillatory interconnecting means between the piston rod and the cylinder to cause the piston and the cylinder to move in phase with each other while permitting variations in the lengths ofsaid power stroke and said compression stroke, and resilient means in the precompression chamber between an outer end of said precompression chamber and the piston to be compressed during said power stroke, said resilient means after the power stroke moving the piston and cylinder towards each other through a compression stroke.

7. A power unit as claimed in claim 6 in which said interconnecting means comprises rack teeth on the piston rod, and a segment gear having first teeth meshing with said rack teeth and second teeth meshing with a rack connected to the cylinder, said segment gear being mountd on a shaft carried by the base.

8. A power unit as claimed in claim 6 including an intake port in the cylinder to direct a combustible fuel into the precompression chamber when the piston is near the end of the compression stroke, a transfer passage for receiving fuel under pressure from the precompression chamber during the power stroke of the piston and directing said pressured fuel into the power chamber as the piston nears the end of the power stroke, and an exhaust port in the cylinder positioned to exhaust gas from the power chamber when the piston nears the end of the power stroke.

9. A power unit as claimed in claim 8 including port means for relieving fuel pressure in the precompression chamber when the piston has moved about as far as possible on the power stroke.

10. A power unit as claimed in claim 6 in which said cylinder is slidably mounted in an outer cylinder so as to pump air over the first-mentioned cylinder during reciprocation thereof in said outer cylinder.

11. In an internal combustion, two-stroke power unit, a base, an elongated cylinder mounted for reciprocation in the base, a piston mounted for reciprocation in the cylinder and dividing said cylinder into a power chamber and a precompression chamber, a piston rod connected to the piston and extending through and out from the precompression chamber, said piston and cylinder being moved away from each other on a power stroke when a fuel charge is fired in the power chamber, interconnecting means between the piston rod and the cylinder to cause the piston and the cylinder to move in phase with each other, means for moving the piston back through a compression stroke, an intake port in the cylinder to direct a combustible fuel into the precompression chamber when the piston is near the end of the compression stroke, a transfer passage for receiving fuel under pressure from the precompression chamber during the power stroke of the piston and directing said pressured fuel into the power chamber as the piston nears the end of the power stroke, said piston compressing the fuel in the precompression chamber during the power stroke, and means for relieving pressure in the precompression chamber as the piston nears the end of the power stroke when under partial and no load conditions.

12. A power unit as claimed in claim 11 in which said pressure relieving means comprises an auxiliary port in the precompression chamber positioned to be closed by the piston as the latter nears the end of the power stroke under full load and to be opened as said piston nears the end of said power stroke under partial and no load conditions. I

13. A power unit as claimed in claim 11 in which said piston is formed with a skirt having a port therein, and said pressure relieving means includes an auxiliary port in the precompression chamber positioned to be closed by the piston skirt as the piston nears the end of the power stroke under full load and to at least partially register with said skirt port as said piston nears the end of said power stroke under partial and no load conditions.

14. A power unit as claimed in claim 13 in which said transfer passage, the skirt port and the precompression chamber port are so positioned relative to each other that said skirt port can being the transfer passage and said chamber port into communication with each other under partial load conditions.

15. In an internal combustion, two-stroke power unit, a base, first and second aligned cylinders mounted for reciprocation in the base, connecting means between the cylinders to cause said cylinders to reciprocate together, a head at an outer end of each cylinder, a wall in each cylinder spaced from the head thereof, first and second pistons reciprocally mounted in the first and second cylinders between the heads and walls thereof, connecting means between the pistons to cause said pistons to reciprocate together, each piston dividing the cylinder in which it is located into a power chamber next to the head and a precompression chamber next to the wall, said first piston moving through a power stroke and the first cylinder moving in the opposite direction when a fuel charge is fired in the chamber of the first cylinder and moving the second piston through a compression stroke in the second cylinder and vice versa, oscillatory interconnecting means between said pistons and said cylinders to cause the piston and cylinders to move in phase with each other during relative reciprocation thereof while permitting variations in the lengths of said poser strokes and said compression stroke, and power take-off means connected to said first and second pistons operable during reciprocation of said pistons.

16. A power unit as claimed in claim 15 in which said connecting means between the pistons comprises a piston rod extending between and secured to said first and second pistons.

17. A power unit as claimed in claim 16 in which said power take-off means comprises first and second linkage between said piston rod and said cylinders, said first linkage driving a first one-way ratchet and said second linkage driving a second one-way ratchet during the relative reciprocation of the pistons and cylinders, said first ratchet operating in the opposite direction to the second ratchet.

18. A power unit as claimed in claim 17 in which each linkage includes a crank arm mounted between ends thereof on a drive shaft for turning one of said ratchets, means connecting one end of the crank arm to the piston rod, and means connecting the opposite end of said arm to the cylinders.

19. A power unit as claimed in claim 18 in which the means connecting said one end of each crank arm to the piston rod comprises a link pivotally connected to said one end and to said piston rod.

20. A power unit as claimed in claim 18 in which the means connecting said opposite end of each crank arm to the cylinders comprises a link pivotally connected to said opposite end and to a bracket connected to said cylinders.

21. A power unit as claimed in claim 18 in which the means connecting said opposite end of each crank arm to the cylinders comprises a spring extending between said opposite end and a bracket connected to said cylinders.

22. A power unit as claimed in claim 18 in the shaft of each crank arm is positioned nearer to said opposite end thereof than to said one end thereof.

23. A power unit as claimed in claim 15 including an intake port in each cylinder to direct a combustible fuel into the precompression chamber thereof, a transfer passage for directing said fuel under pressure from the precompression chamber of said each cylinder to the power chamber of the latter cylinder, and an exhaust port in said each cylinder positioned to exhaust gas therefrom when the piston in the latter cylinder nears the end of its power stroke.

24. A power unit as claimed in claim 15 in which said interconnecting means comprises a rack and pinion means connected to the pistons and to the cylinders.

25. A power unit as claimed in claim 16 in which said interconnecting means comprises a rack connected to said piston rod, and a segment gear connected to the cylinders, and meshing with said rack, said segment gear being mounted on a shaft carried by the base.

26. A power unit as claimed in claim in which said segment gear is eccentrically mounted on the shaft, said segment gear having first teeth meshing with said rack and second teeth closer to said shaft than the first teeth and meshing with a rack connected to the cylinders.

27. A power unit as claimed in claim 26 in which said second-mentioned rack is connected to the cylinders through a spring.

28. A power unit as claimed in claim 6 including means for selectively and releasably locking said piston and cylinder against relative movement when said spring means is compressed.

29. A power unit as claimed in claim 16 in which said power take-off means comprises a take-off piston mounted for reciprocation in a cylinder connected to said base and extending substantially at right angles to said piston rod, a rod connected to the take-off piston and extending out through an outer end of the take-off piston cylinder, and a connecting link connected at one end to the take-off piston and at an opposite end to the piston rod, said connecting link being of such length that reciprocation of the piston rod causes the take-off piston to reciprocate in the cylinder thereof.

30. A power unit as claimed in claim 28 in which said locking means comprises a gear fixed on a shaft and meshing with teeth on said piston rod, an arm fixed to said shaft, and a control lever swingably mounted on the base and having ratchet teeth thereon normally engaged by the arm to prevent rotation of said gear, said lever being swingable to move the teeth away from the arm to release said gear.

31. A power unit as claimed in claim 28 in which said locking means comprises a ratchet arm having ratchet teeth thereon adapted to engage ratchet teeth in said piston rod when the piston is at the end of a power stroke, spring means normally urging said arm towards the piston rod, and trigger means connected to said spring means operable to draw the ratchet arm away from the piston rod.

32. A power unit as claimed in claim 31 including a slide on the ratchet arm, a pivotally mounted lever adjacent said arm, an extension pivotally connected to the lever, pin means connecting the slide to the extension and extending through slot means in the lever, and a spring connected to the extension to permit rocking movement thereof.

33. A power unit as claimed in claim 32 in which said spring means comprises a spring connected at one end to said slide and having a free end normally fitting in a notch in the ratchet arm.

34. A power unit as claimed in claim 33 in which said trigger means comprises a pivotal! mounted trigger connected to the ree end of sa1 spring by ca le means.

35. A power unit as claimed in claim 12 in which said intake port and said auxiliary port communicate with a base of the power unit, and including carbureting means having an outlet connected to said base for directing the combustible fuel thereinto.

36. In an internal combustion, two-stroke power unit, a base, a cylinder element mounted for reciprocation in the base, a piston element mounted for reciprocation in the cylinder element, said piston and cylinder elements being moved away from each other on a power stroke when a fuel charge is fired in the cylinder element, resilient means between the piston and cylinder elements and positioned to be compressed during said power stroke, said resilient means after the power stroke moving said elements towards each other through a compression stroke, oscillatory interconnecting means between the cylinder element and the piston element to cause said elements to move in phase with each other while permitting variations in the lengths of said power stroke and said compression stroke, and power take-off means connected to one of said elements operable on relative reciprocation of the piston and cylinder elements. 

1. In an internal combustion, two-stroke power unit, a base, a cylinder element mounted for reciprocation in the base, a piston element mounted for reciprocation in the cylinder element, said piston and cylinder elements being moved away from each other on a power stroke when a fuel charge is fired in the cylinder element resilient means between the piston and cylinder elements and positioned to be compressed during said power stroke, said resilient means after the power stroke moving said elements towards each other through a compression stroke, interconnecting means between the cylinder element anD the piston element to cause said elements to work in phase with each other, and power take-off means connected to one of said elements operable on relative reciprocation of the piston and cylinder elements, said interconnecting means comprising a rack connected to the piston element and a segment gear eccentrically mounted on a shaft carried by the base, said segment gear having first teeth meshing with said rack and second teeth closer to said shaft than the first teeth and meshing with a rack connected to the cylinder element.
 2. In an internal combustion two-stroke power unit, a base, a cylinder element mounted for reciprocation in the base, a piston element mounted for reciprocation in the cylinder element, said piston and cylinder elements being moved away from each other on a power stroke when a fuel charge is fired in the cylinder element, resilient means between the piston and cylinder elements and positioned to be compressed during said power stroke, said resilient means, after the power stroke, moving said elements towards each other through a compression stroke, oscillatory interconnecting means between the cylinder element and the piston element to cause said elements to move in phase with each other while permitting variations in the lengths of said power stroke and said compression stroke; and power take-off means connected to one of said elements operable on relative reciprocation of the piston and cylinder elements, said cylinder element being slidably mounted in an outer cylinder forming part of said base, said cylinder element pumping air over the outer surface thereof during reciprocation in said outer cylinder.
 3. In an internal combustion, two-stroke power unit, a base, a cylinder element mounted for reciprocation in the base, a piston element mounted for reciprocation in the cylinder element, said piston and cylinder elements being moved away from each other on a power stroke when a fuel charge is fired in the cylinder element resilient means between the piston and cylinder elements and positioned to be compressed during said power stroke, said resilient means after the power stroke moving said elements towards each other through a compression stroke, oscillatory interconnecting means between the cylinder element and the piston element to cause said elements to move inphase with each other while permitting variations in the lengths of said power stroke and said compression stroke, and power take-off means connected to one of said elements operable on relative reciprocation of the piston and cylinder elements, said cylinder element having a head at one end and a precompression chamber at the opposite end thereof and including an intake port in the cylinder element to direct a combustible fuel into said precompression chamber when said piston element is near said head, a transfer passage for directing said fuel under pressure from the precompression chamber into the cylinder element between said head and the piston element during said power stroke, and an exhaust port in the cylinder element positioned to exhaust gas from said cylinder element when the piston element nears the end of the power stroke.
 4. A power unit as claimed in claim 3 in which said piston element has a skirt opening towards said precompression chamber, said skirt having a port therein positioned to keep the transfer passage in communication with the precompression chamber during at least part of the power stroke.
 5. A power unit as claimed in claim 4 in which said skirt port is positioned substantially to register with an auxiliary port in the precompression chamber as the piston element moves about as far as possible on the power stroke to relieve the pressure in the precompression chamber.
 6. In an internal combustion, two-stroke power unit, a base, an elongated cylinder mounted for reciprocation in the base, a piston mounted for reciprocation in the cylinder and dividing said cylinder into a power chamber and a precompression chamber, a piston rod connected to the piston and extEnding through and out from the precompression chamber, said piston and cylinder being moved away from each other on a power stroke when a fuel charge is fired in the power chamber, oscillatory interconnecting means between the piston rod and the cylinder to cause the piston and the cylinder to move in phase with each other while permitting variations in the lengths of said power stroke and said compression stroke, and resilient means in the precompression chamber between an outer end of said precompression chamber and the piston to be compressed during said power stroke, said resilient means after the power stroke moving the piston and cylinder towards each other through a compression stroke.
 7. A power unit as claimed in claim 6 in which said interconnecting means comprises rack teeth on the piston rod, and a segment gear having first teeth meshing with said rack teeth and second teeth meshing with a rack connected to the cylinder, said segment gear being mounted on a shaft carried by the base.
 8. A power unit as claimed in claim 6 including an intake port in the cylinder to direct a combustible fuel into the precompression chamber when the piston is near the end of the compression stroke, a transfer passage for receiving fuel under pressure from the precompression chamber during the power stroke of the piston and directing said pressured fuel into the power chamber as the piston nears the end of the power stroke, and an exhaust port in the cylinder positioned to exhaust gas from the power chamber when the piston nears the end of the power stroke.
 9. A power unit as claimed in claim 8 including port means for relieving fuel pressure in the precompression chamber when the piston has moved about as far as possible on the power stroke.
 10. A power unit as claimed in claim 6 in which said cylinder is slidably mounted in an outer cylinder so as to pump air over the first-mentioned cylinder during reciprocation thereof in said outer cylinder.
 11. In an internal combustion, two-stroke power unit, a base, an elongated cylinder mounted for reciprocation in the base, a piston mounted for reciprocation in the cylinder and dividing said cylinder into a power chamber and a precompression chamber, a piston rod connected to the piston and extending through and out from the precompression chamber, said piston and cylinder being moved away from each other on a power stroke when a fuel charge is fired in the power chamber, interconnecting means between the piston rod and the cylinder to cause the piston and the cylinder to move in phase with each other, means for moving the piston back through a compression stroke, an intake port in the cylinder to direct a combustible fuel into the precompression chamber when the piston is near the end of the compression stroke, a transfer passage for receiving fuel under pressure from the precompression chamber during the power stroke of the piston and directing said pressured fuel into the power chamber as the piston nears the end of the power stroke, said piston compressing the fuel in the precompression chamber during the power stroke, and means for relieving pressure in the precompression chamber as the piston nears the end of the power stroke when under partial and no load conditions.
 12. A power unit as claimed in claim 11 in which said pressure relieving means comprises an auxiliary port in the precompression chamber positioned to be closed by the piston as the latter nears the end of the power stroke under full load and to be opened as said piston nears the end of said power stroke under partial and no load conditions.
 13. A power unit as claimed in claim 11 in which said piston is formed with a skirt having a port therein, and said pressure relieving means includes an auxiliary port in the precompression chamber positioned to be closed by the piston skirt as the piston nears the end of the power stroke under full load and to at least partially register with said skirt port as said piston nears the end of said power stroke under partIal and no load conditions.
 14. A power unit as claimed in claim 13 in which said transfer passage, the skirt port and the precompression chamber port are so positioned relative to each other that said skirt port can being the transfer passage and said chamber port into communication with each other under partial load conditions.
 15. In an internal combustion, two-stroke power unit, a base, first and second aligned cylinders mounted for reciprocation in the base, connecting means between the cylinders to cause said cylinders to reciprocate together, a head at an outer end of each cylinder, a wall in each cylinder spaced from the head thereof, first and second pistons reciprocally mounted in the first and second cylinders between the heads and walls thereof, connecting means between the pistons to cause said pistons to reciprocate together, each piston dividing the cylinder in which it is located into a power chamber next to the head and a precompression chamber next to the wall, said first piston moving through a power stroke and the first cylinder moving in the opposite direction when a fuel charge is fired in the chamber of the first cylinder and moving the second piston through a compression stroke in the second cylinder and vice versa, oscillatory interconnecting means between said pistons and said cylinders to cause the piston and cylinders to move in phase with each other during relative reciprocation thereof while permitting variations in the lengths of said poser strokes and said compression stroke, and power take-off means connected to said first and second pistons operable during reciprocation of said pistons.
 16. A power unit as claimed in claim 15 in which said connecting means between the pistons comprises a piston rod extending between and secured to said first and second pistons.
 17. A power unit as claimed in claim 16 in which said power take-off means comprises first and second linkage between said piston rod and said cylinders, said first linkage driving a first one-way ratchet and said second linkage driving a second one-way ratchet during the relative reciprocation of the pistons and cylinders, said first ratchet operating in the opposite direction to the second ratchet.
 18. A power unit as claimed in claim 17 in which each linkage includes a crank arm mounted between ends thereof on a drive shaft for turning one of said ratchets, means connecting one end of the crank arm to the piston rod, and means connecting the opposite end of said arm to the cylinders.
 19. A power unit as claimed in claim 18 in which the means connecting said one end of each crank arm to the piston rod comprises a link pivotally connected to said one end and to said piston rod.
 20. A power unit as claimed in claim 18 in which the means connecting said opposite end of each crank arm to the cylinders comprises a link pivotally connected to said opposite end and to a bracket connected to said cylinders.
 21. A power unit as claimed in claim 18 in which the means connecting said opposite end of each crank arm to the cylinders comprises a spring extending between said opposite end and a bracket connected to said cylinders.
 22. A power unit as claimed in claim 18 in the shaft of each crank arm is positioned nearer to said opposite end thereof than to said one end thereof.
 23. A power unit as claimed in claim 15 including an intake port in each cylinder to direct a combustible fuel into the precompression chamber thereof, a transfer passage for directing said fuel under pressure from the precompression chamber of said each cylinder to the power chamber of the latter cylinder, and an exhaust port in said each cylinder positioned to exhaust gas therefrom when the piston in the latter cylinder nears the end of its power stroke.
 24. A power unit as claimed in claim 15 in which said interconnecting means comprises a rack and pinion means connected to the pistons and to the cylinders.
 25. A power unit as claimed in claim 16 in which said interconnecting means coMprises a rack connected to said piston rod, and a segment gear connected to the cylinders, and meshing with said rack, said segment gear being mounted on a shaft carried by the base.
 26. A power unit as claimed in claim 25 in which said segment gear is eccentrically mounted on the shaft, said segment gear having first teeth meshing with said rack and second teeth closer to said shaft than the first teeth and meshing with a rack connected to the cylinders.
 27. A power unit as claimed in claim 26 in which said second-mentioned rack is connected to the cylinders through a spring.
 28. A power unit as claimed in claim 6 including means for selectively and releasably locking said piston and cylinder against relative movement when said spring means is compressed.
 29. A power unit as claimed in claim 16 in which said power take-off means comprises a take-off piston mounted for reciprocation in a cylinder connected to said base and extending substantially at right angles to said piston rod, a rod connected to the take-off piston and extending out through an outer end of the take-off piston cylinder, and a connecting link connected at one end to the take-off piston and at an opposite end to the piston rod, said connecting link being of such length that reciprocation of the piston rod causes the take-off piston to reciprocate in the cylinder thereof.
 30. A power unit as claimed in claim 28 in which said locking means comprises a gear fixed on a shaft and meshing with teeth on said piston rod, an arm fixed to said shaft, and a control lever swingably mounted on the base and having ratchet teeth thereon normally engaged by the arm to prevent rotation of said gear, said lever being swingable to move the teeth away from the arm to release said gear.
 31. A power unit as claimed in claim 28 in which said locking means comprises a ratchet arm having ratchet teeth thereon adapted to engage ratchet teeth in said piston rod when the piston is at the end of a power stroke, spring means normally urging said arm towards the piston rod, and trigger means connected to said spring means operable to draw the ratchet arm away from the piston rod.
 32. A power unit as claimed in claim 31 including a slide on the ratchet arm, a pivotally mounted lever adjacent said arm, an extension pivotally connected to the lever, pin means connecting the slide to the extension and extending through slot means in the lever, and a spring connected to the extension to permit rocking movement thereof.
 33. A power unit as claimed in claim 32 in which said spring means comprises a spring connected at one end to said slide and having a free end normally fitting in a notch in the ratchet arm.
 34. A power unit as claimed in claim 33 in which said trigger means comprises a pivotally mounted trigger connected to the free end of said spring by cable means.
 35. A power unit as claimed in claim 12 in which said intake port and said auxiliary port communicate with a base of the power unit, and including carbureting means having an outlet connected to said base for directing the combustible fuel thereinto.
 36. In an internal combustion, two-stroke power unit, a base, a cylinder element mounted for reciprocation in the base, a piston element mounted for reciprocation in the cylinder element, said piston and cylinder elements being moved away from each other on a power stroke when a fuel charge is fired in the cylinder element, resilient means between the piston and cylinder elements and positioned to be compressed during said power stroke, said resilient means after the power stroke moving said elements towards each other through a compression stroke, oscillatory interconnecting means between the cylinder element and the piston element to cause said elements to move in phase with each other while permitting variations in the lengths of said power stroke and said compression stroke, and power take-off means connected to one of said elements operable on relative reciprocation of the piston and cylinder elements. 